The present invention relates to an on-board electric power supply system which supplies DC power to various loads in an automobile, and particularly to an on-board electric power supply system which reduces the voltage variation in load driving by application of a predetermined voltage and supply of a desired current (hereinafter, often referred to as a DC supply) from a battery.
In a recent DC power supply system for an automobile, a voltage converter (DC/DC converter) is employed in order to stably supply 12-volt DC (hereinafter, often referred to as a low-voltage system) which is conventionally used for lamps, vehicle-mounted electronic apparatuses, etc. Furthermore, a DC supply for a blower motor which efficiently operates at a relatively high voltage, and a supply of, for example, 48-volt DC at which a large power supply can be performed by using a thin cable conductor (hereinafter, such a DC supply is often referred to as a high-voltage system) are known (for example, Japanese unexamined Patent Publication Hei. 5-278535 xe2x80x9cElectric power supply system for automotive vehiclexe2x80x9d).
FIG. 3 is a block diagram showing the configuration of a conventional on-board electric power supply system having such low- and high-voltage systems.
In the on-board electric power supply system, a DC voltage from a alternator 2 charges a battery 3 of a high-voltage system (for example, 48 volts). The DC voltage of the high-voltage system is supplied to a blower motor 4 via a switch SW1, and also to a voltage converter 5 so as to be subjected to low-voltage conversion to 12-volt DC. The converted low voltage charges a battery 6 of a low-voltage system (12 volts).
The low voltage of the battery 6 is supplied to a load 10 (a switch SW2 and a lamp 10a, a vehicle speed sensor 10b, a switch SW3 and a bleeder resistor R, and the like). In the on-board electric power supply system, the voltage and the current of the battery 6 are detected by a voltage detector 7 and a current detector 8. Only when the voltage of the battery 6 is lowered to a level below a specified value, particularly, a controller 9 activates the voltage converter 5 to charge the battery 6. Namely, the current consumption can be reduced in accordance with the operation/inoperation of the voltage converter 5.
A vehicle that includes such a DC supply is performed with an electric junction box of a multi-layer structure in which circuit boards are stacked and harness connectors, fuses for loads, and switching devices are incorporated so as to realize electrical connection. The electric junction box provides a DC supply to the loads such as lamps, motors, and vehicle-mounted electronic apparatuses (for example, an audio apparatus, a navigation apparatus, and a television receiver), simplifies the connection wiring using concentrated wiring, and facilitates maintenance works.
In an electric junction box, a well-known configuration may be employed in which a CPU for executing multiplex transmission (for example, time division multiple access (TDMA)) using a local area network (LAN) is incorporated in order to implement DC branching and recent complicated vehicle controls (for example, various controls on an increased number of vehicle-mounted electronic apparatuses, and an elaborated air-fuel ratio control). The CPU captures various multiplex signals (for examples, signals instructing on/off operations and function change over of vehicle-mounted electronic apparatuses), and switches over the switching devices, thereby controlling activation and inactivation (on and off) of each load.
FIG. 4 is a timing chart illustrating the operation of the conventional on-board electric power supply system.
As shown in (a) of FIG. 4, the CPU captures an operation signal (SW signal) at a time T, and executes an ON control on a switching device for the corresponding load channel. When a large inrush current to a lamp or the like is generated as a result of the ON control as shown in (b) of FIG. 4, a DC voltage (hereinafter, often referred to as a battery voltage) which is to be supplied from a battery to a load is temporarily dropped by the large inrush current when power supply to the load is activated. After a delay from the voltage drop, an activation control for supplying a DC output from the voltage converter 5 to the battery is executed so as to compensate for the voltage drop. Therefore, the voltage drop shown in (c) of FIG. 4 may cause the illumination of a lamp to be lowered for a moment, or an audio output to be temporarily reduced.
As described above, the on-board electric power supply system of the conventional art example has a defect that, when the power supply in, particularly, a 12-V low-voltage system is turned on, voltage variation of a relatively large level is generated as a result of driving of a load, so that the illumination of a lamp is lowered for a moment or an audio output is temporarily reduced.
The invention has been conducted in order to solve the problem of the related art. It is an object of the invention to provide an on-board electric power supply system in which voltage variation due to driving of a load in a DC supply from a battery upon turning on of a power supply can be accurately suppressed to a minimum level, overcharge can be prevented from occurring, and power consumption can be reduced.
In order to attain the object, the on-board electric power supply system of the invention is configured so that the system comprises: a battery which performs a DC power supply at a predetermined voltage and a required current to plural loads; voltage converting means for performing a DC power supply to the battery while converting an input DC voltage; and controlling means for, immediately after an ON control signal instructing activation of a load is captured, performing activation of the voltage converting means.
Furthermore, the on-board electric power supply system of the invention is configured so that the system comprises: a battery which performs a DC power supply at a predetermined voltage and a required current to plural loads; voltage converting means for performing a DC power supply to the battery while converting an input DC voltage; and controlling means for, immediately after an ON control signal instructing activation of a load is captured, performing a DC power supply corresponding to prestored information of power consumption of the load which is instructed to be activated, by activating and controlling the voltage converting means.
Preferably, the controlling means comprises timer means, the timer means counts a time elapsed after a control of turning off a load, the controlling means estimates an inrush current from a temperature state of the load at the elapsed time, and a DC supply corresponding to the estimated inrush current is performed from the voltage converting means to the load under a control of the controlling means.
In the thus configured on-board electric power supply system of the invention, a control of activating the voltage converting means is performed immediately after an ON control signal instructing activation of a load is captured. Together with the activation control, a DC supply corresponding to the prestored power consumption of the load is performed. As a result, voltage variation due to driving of a load in a DC supply from the battery upon turning on a power supply, i.e., an inrush current at the start of activation of the load can be accurately suppressed to a minimum level.
In the on-board electric power supply system of the invention, a DC output is performed on the basis of the temperature state of a load which corresponds to the time elapsed after a control of turning off the load. When the temperature of the load is low, for example, the resistance is low so that the inrush current of the load is large.
The controlling means controls the voltage converting means so as to perform a DC supply corresponding to the low temperature. As a result, it is not required to perform the charge control on the battery in excess of that needed, so that overcharge can be prevented from occurring and power consumption can be reduced.
In the case where the load is a lamp or the like, particularly, an inrush current is remarkably changed with respect the temperature state, and a large inrush current flows when the temperature is low. When an ON/OFF control or the like is performed, therefore, the duty ratio in an initial state is largely different from that in a state where the lamp is warmed.